1. Field of the Invention
This invention generally relates to a servo-system or servomechanism, and particularly to a digitally controlled electrical servo-system for controlling the operating time period of a servo-motor. More specifically, the present invention is concerned with an incremental servo-control system including a servo-motor which may, for example, be used as a selection motor for driving to rotate a print wheel to have a selected type located at a predetermined printing position, a motor for driving to move a carriage carrying thereon a printing head along a platen roller in a reciprocating manner, or a motor for driving to move an optical system in a copier for scanning an original placed on an original holder.
2. Description of the Prior Art
A servo-system is basically an automatic feedback system which allows the controlled quantity or output, defined by a variance in position, orientation, velocity and the like of a target, to follow arbitrary changes in the target value or input. The controlled quantity in the servo-system implies a mechanical variance such as position, velocity and acceleration in contrast to state variables such as temperature, density and pressure which are of concern in the process control.
In adjusting the velocity of a servo-motor, it has conventionally been proposed to use such elements as potentiometers, jumpers and switches. However, if use is made of a potentiometer, an operator is required to adjust the potentiometer appropriately while measuring the real velocity or operating time period of servo-motor which is time consuming and expensive. Moreover, if the velocity must be readjusted due, for example, to maintenance of apparatus, resetting of potentiometer is also required. In addition, potentiometers are expensive as compared with fixed resistors. Use of jumpers and switches is equally unpromising because a great number of such elements must be provided if it is desired to carry out fine adjustments, which tends to push up cost and occupy a larger mounting space. Thus, there has been a need to develop an adjustable servo-system which is easy to operate, simple and compact in size and thus less expensive to make.